1. Technical Field
The present disclosure relates to an illumination controlling circuit. More particularly, the present disclosure relates to an illumination controlling circuit with dimming functions.
2. Description of Related Art
With recent development of the photonics technology, many cutting-edge illumination equipments have been introduced to our daily life. For example, comprehensive attentions have been paid on fluorescent lamps and light-emitting diodes (LED) and their applications.
Among those equipments, a LED lamp has an efficiency superior to a traditional incandescent lamp, because most energy consumed by the LED lamp is transformed into a visible radiation. The LED lamp has a photoelectric conversion efficiency far higher than that of other lamps, and the LED lamps generates less heat during operation. Therefore, under a condition of same luminance, the LED lamp with a higher light-emitting efficiency has a lower operative temperature than that of the traditional incandescent lamp, such that the LED lamp suitable for the green-energy trend is widely used in all kinds of illumination applications.
Traditional incandescent lamps are usually cooperated with a tri-electrode alternating-current switch (TRIAC) dimmer, which is conveniently for users to adjust luminance of the incandescent lamps themselves, so as to prevent wasting energy and possible uncomfortable feelings of eyes due to the over-brightness. In general, the TRIAC may include a variable resistor, in which a resistance can be adjusted (e.g., with rotating a knob of the TRIAC) by users. In this way, users are able to control a conductive angel of the TRIAC, so as to change an output waveform of the TRIAC.
The dimming function of the TRIAC is realized in a phase-chopping manner. Reference is made to FIG. 1, which is a schematic diagram illustrating a dimming signal waveform generated by a tradition TRIAC dimmer. In FIG. 1, the waveform generated by the TRIAC is chopped according to its phases, and the dimming result is related to the conductive angle of the phase-chopping.
However, the LED lamp is a direct current (DC) load unlike the incandescent lamps, and thus is unable to directly apply the dimming function of the TRIAC. The LED lamp, directly driven by a waveform adjusted by the TRIAC dimmer, will blinks at a high frequency. Besides, when the dimming brightness is configured lower, the blinking becomes more severe. Therefore, an adjustable contrast range of the LED lamp with the TRIAC dimmer is limited.
Currently, the commercialized LED equipments utilize specific LED drivers for transforming household electricity into a fixed DC voltage signal, which is used to drive the light-emitting component in the LED for illumination. The DC voltage signal is set at a fixed voltage level. Therefore, the luminance cannot be adjusted easily. In order to keep up with the green-energy trend and users' demands, there is still a need to develop LED illumination equipments with practical dimming function.